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  </header><main class="col-sm-12 col-md-9 col-lg-7" id="content"><div id="m" class="section level1" number="14">
<h1>
<span class="header-section-number">14</span> M<a class="anchor" aria-label="anchor" href="#m"><i class="fas fa-link"></i></a>
</h1>

<div id="markdown" class="section level2" number="14.1">
<h2>
<span class="header-section-number">14.1</span> markdown<a class="anchor" aria-label="anchor" href="#markdown"><i class="fas fa-link"></i></a>
</h2>
<p><dfn>A way to specify formatting, such as headers, paragraphs, lists, bolding, and links.</dfn></p>
<p>See <a href="r.html#r-markdown">R Markdown</a> for more infomation on the R-specific version.</p>

</div>
<div id="mask" class="section level2" number="14.2">
<h2>
<span class="header-section-number">14.2</span> mask<a class="anchor" aria-label="anchor" href="#mask"><i class="fas fa-link"></i></a>
</h2>
<p><dfn>When two packages have functions with the same name, the function from the package loaded last is used as the default unless the package name is also specified.</dfn></p>
<p>See <a href="c.html#conflict">conflict</a>.</p>

</div>
<div id="match-operator" class="section level2" number="14.3">
<h2>
<span class="header-section-number">14.3</span> match operator<a class="anchor" aria-label="anchor" href="#match-operator"><i class="fas fa-link"></i></a>
</h2>
<p><dfn>A binary operator (%in%) that returns a logical vector indicating if there is a match or not for its left operand.</dfn></p>
<div class="sourceCode" id="cb136"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span class="co"># check if a single value is in a vector</span>
<span class="st">"West Dakota"</span> <span class="op">%in%</span> <span class="va">state.name</span>
<span class="co">#&gt; [1] FALSE</span></code></pre></div>
<div class="sourceCode" id="cb137"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span class="co"># check if each item in the lefthand vector is in the righthand vector</span>
<span class="fu"><a href="https://rdrr.io/r/base/c.html">c</a></span><span class="op">(</span><span class="st">"A"</span>, <span class="st">"B"</span>, <span class="st">"1"</span><span class="op">)</span> <span class="op">%in%</span> <span class="va">LETTERS</span>
<span class="co">#&gt; [1]  TRUE  TRUE FALSE</span></code></pre></div>
<div class="sourceCode" id="cb138"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span class="va">pangram</span> <span class="op">&lt;-</span> <span class="st">"the quick brown fox jumps over the lazy dog"</span>
<span class="va">pangram_chars</span> <span class="op">&lt;-</span> <span class="fu"><a href="https://rdrr.io/r/base/strsplit.html">strsplit</a></span><span class="op">(</span><span class="va">pangram</span>, <span class="st">""</span><span class="op">)</span><span class="op">[[</span><span class="fl">1</span><span class="op">]</span><span class="op">]</span>
<span class="va">letters</span> <span class="op">%in%</span> <span class="va">pangram_chars</span>
<span class="co">#&gt;  [1] TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE</span>
<span class="co">#&gt; [25] TRUE TRUE</span></code></pre></div>

</div>
<div id="matrix" class="section level2" number="14.4">
<h2>
<span class="header-section-number">14.4</span> matrix<a class="anchor" aria-label="anchor" href="#matrix"><i class="fas fa-link"></i></a>
</h2>
<p><dfn>A <a href="c.html#container">container</a> data type consisting of numbers arranged into a fixed number of rows and columns</dfn></p>
<p>You can use the <code><a href="https://rdrr.io/r/base/matrix.html">matrix()</a></code> function to set up a <a href="v.htm#vector">vector</a> of numbers as a matrix with a specified number of rows of columns.</p>
<div class="sourceCode" id="cb139"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span class="co"># a 4x4 matrix</span>
<span class="fu"><a href="https://rdrr.io/r/base/matrix.html">matrix</a></span><span class="op">(</span>data <span class="op">=</span> <span class="fl">1</span><span class="op">:</span><span class="fl">16</span>, nrow <span class="op">=</span> <span class="fl">4</span><span class="op">)</span>
<span class="co">#&gt;      [,1] [,2] [,3] [,4]</span>
<span class="co">#&gt; [1,]    1    5    9   13</span>
<span class="co">#&gt; [2,]    2    6   10   14</span>
<span class="co">#&gt; [3,]    3    7   11   15</span>
<span class="co">#&gt; [4,]    4    8   12   16</span></code></pre></div>
<p>Set <code>byrow = TRUE</code> to assign the vector across rows rather than down columns.</p>
<div class="sourceCode" id="cb140"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span class="fu"><a href="https://rdrr.io/r/base/matrix.html">matrix</a></span><span class="op">(</span>data <span class="op">=</span> <span class="fl">1</span><span class="op">:</span><span class="fl">16</span>, nrow <span class="op">=</span> <span class="fl">4</span>, byrow <span class="op">=</span> <span class="cn">TRUE</span><span class="op">)</span>
<span class="co">#&gt;      [,1] [,2] [,3] [,4]</span>
<span class="co">#&gt; [1,]    1    2    3    4</span>
<span class="co">#&gt; [2,]    5    6    7    8</span>
<span class="co">#&gt; [3,]    9   10   11   12</span>
<span class="co">#&gt; [4,]   13   14   15   16</span></code></pre></div>

</div>
<div id="mean" class="section level2" number="14.5">
<h2>
<span class="header-section-number">14.5</span> mean<a class="anchor" aria-label="anchor" href="#mean"><i class="fas fa-link"></i></a>
</h2>
<p><dfn>A <a href="d.html#descriptive">descriptive</a> statistic that measures the average value of a set of numbers.</dfn></p>
<div class="sourceCode" id="cb141"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span class="va">x</span> <span class="op">&lt;-</span> <span class="fu"><a href="https://rdrr.io/r/base/c.html">c</a></span><span class="op">(</span><span class="fl">3</span>,<span class="fl">5</span>,<span class="fl">8</span>,<span class="fl">9</span>,<span class="fl">11</span><span class="op">)</span>
<span class="fu"><a href="https://rdrr.io/r/base/mean.html">mean</a></span><span class="op">(</span><span class="va">x</span><span class="op">)</span>
<span class="co">#&gt; [1] 7.2</span></code></pre></div>

</div>
<div id="median" class="section level2" number="14.6">
<h2>
<span class="header-section-number">14.6</span> median<a class="anchor" aria-label="anchor" href="#median"><i class="fas fa-link"></i></a>
</h2>
<p><dfn>The middle number in a distribution where half of the values are larger and half are smaller.</dfn></p>
<div class="sourceCode" id="cb142"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span class="va">values</span> <span class="op">&lt;-</span> <span class="fu"><a href="https://rdrr.io/r/base/c.html">c</a></span><span class="op">(</span><span class="fl">1</span>, <span class="fl">1</span>, <span class="fl">1</span>, <span class="fl">2</span>, <span class="fl">3</span>, <span class="fl">5</span>, <span class="fl">6</span>, <span class="fl">9</span>, <span class="fl">9</span><span class="op">)</span>

<span class="co"># calculate the median of the values</span>
<span class="fu"><a href="https://rdrr.io/r/stats/median.html">median</a></span><span class="op">(</span><span class="va">values</span><span class="op">)</span>
<span class="co">#&gt; [1] 3</span></code></pre></div>

</div>
<div id="mixed-design" class="section level2" number="14.7">
<h2>
<span class="header-section-number">14.7</span> mixed design<a class="anchor" aria-label="anchor" href="#mixed-design"><i class="fas fa-link"></i></a>
</h2>
<p><dfn>An experimental design that has both <a href="w.html#within-subject">within-subject</a> and <a href="b.html#between-subject">between-subject</a> <a href="f.html#factor">factors</a>.</dfn></p>
<p>For example, imagine an experiment where you test half of subjects in a dark room with easy, medium, and hard tasks, and the other half in a light room with easy and hard tasks. This experiment has two <a href="f.html#factor">factors</a>: room darkness and task difficulty. The factor of room darkness is <a href="b.html#between-subjects">between subjects</a> and has two <a href="l.html#level">levels</a>: dark and light. The factor of task difficulty is <a href="w.html#within-subjects">within subjects</a> has three levels: easy, medium, and hard. Because this experiment has both within- and between-subject factors, it is described as having a <strong>mixed design</strong>.</p>

</div>
<div id="multilevel-model" class="section level2" number="14.8">
<h2>
<span class="header-section-number">14.8</span> multilevel model<a class="anchor" aria-label="anchor" href="#multilevel-model"><i class="fas fa-link"></i></a>
</h2>
<p><dfn>A type of regression model that involves estimating both <a href="f.html#fixed-effect">fixed effects</a> and <a href="r.html#random-effect">random effects</a>.</dfn></p>
<p>See <a href="l.html#linear-mixed-effects-model">linear mixed effects model</a>.</p>

</div>
<div id="multilevel" class="section level2" number="14.9">
<h2>
<span class="header-section-number">14.9</span> multilevel<a class="anchor" aria-label="anchor" href="#multilevel"><i class="fas fa-link"></i></a>
</h2>
<p><dfn>(or <em>multi-level</em>) Relating to datasets where there are multiple observations taken on the same variable on the same sampling units (usually subjects or stimuli).</dfn></p>
<p>A multilevel dataset is one where there are <a href="r.html#repeated-measures">repeated measurements</a> on the same subjects on the same <a href="v.html#variable">variable</a>. If you have multiple measurements on the same subjects but on <em>different</em> variables, with no more than one measurement per subject per variable, you have <em><a href="m.html#multivariate">multivariate</a></em> data, not multilevel data. It is called "multilevel" because different measurements might be taken at different levels. For example, in a simple reaction time study, you may measure how quickly someone presses a button in response to a flashing light. You can have measurements at the level of the individual trial (the intensity of the flash) as well as measurements at the level of the individual subject (the subject's age in years).</p>
<p>A multilevel model is one that can account for the variance introduced at the various levels.</p>
<p>See also <a href="r.html#repeated-measures">repeated measures</a>.</p>

</div>
<div id="multivariate" class="section level2" number="14.10">
<h2>
<span class="header-section-number">14.10</span> multivariate<a class="anchor" aria-label="anchor" href="#multivariate"><i class="fas fa-link"></i></a>
</h2>
<p><dfn>Having multiple measurements on the same subjects but on <em>different</em> variables, with no more than one measurement per subject per variable.</dfn></p>
<div class="inline-table"><table class="table table-sm">
<caption>
<span id="tab:unnamed-chunk-237">Table 14.1: </span>Multivariate data with 3 scores on different tasks per person
</caption>
<thead><tr>
<th style="text-align:left;">
id
</th>
<th style="text-align:right;">
stroop
</th>
<th style="text-align:right;">
memory
</th>
<th style="text-align:right;">
iat
</th>
</tr></thead>
<tbody>
<tr>
<td style="text-align:left;">
S1
</td>
<td style="text-align:right;">
14
</td>
<td style="text-align:right;">
78
</td>
<td style="text-align:right;">
7
</td>
</tr>
<tr>
<td style="text-align:left;">
S2
</td>
<td style="text-align:right;">
12
</td>
<td style="text-align:right;">
72
</td>
<td style="text-align:right;">
5
</td>
</tr>
<tr>
<td style="text-align:left;">
S3
</td>
<td style="text-align:right;">
10
</td>
<td style="text-align:right;">
76
</td>
<td style="text-align:right;">
5
</td>
</tr>
<tr>
<td style="text-align:left;">
S4
</td>
<td style="text-align:right;">
10
</td>
<td style="text-align:right;">
76
</td>
<td style="text-align:right;">
4
</td>
</tr>
<tr>
<td style="text-align:left;">
S5
</td>
<td style="text-align:right;">
13
</td>
<td style="text-align:right;">
81
</td>
<td style="text-align:right;">
6
</td>
</tr>
</tbody>
</table></div>
<p>Contrast with <a href="u.html#univariate">univariate</a>.</p>

</div>
<div id="mutating-joins" class="section level2" number="14.11">
<h2>
<span class="header-section-number">14.11</span> mutating joins<a class="anchor" aria-label="anchor" href="#mutating-joins"><i class="fas fa-link"></i></a>
</h2>
<p><dfn><a href="j.html#joins">Joins</a> that act like the <code><a href="https://dplyr.tidyverse.org/reference/mutate.html">dplyr::mutate()</a></code> function in that they add new columns to one table based on values in another table.</dfn></p>
<ul>
<li><a href="l.html#left-join">left_join</a></li>
<li><a href="r.html#right-join">right_join</a></li>
<li><a href="i.html#inner-join">inner_join</a></li>
<li><a href="f.html#full-join">full_join</a></li>
</ul>
</div>
</div>
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<li><a class="nav-link" href="#m"><span class="header-section-number">14</span> M</a></li>
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